1. Field of the Invention
The invention relates to an arrangement in a snowmobile equipped with an apparatus for intensifying steering, which intensifying apparatus consists of the ski of the snowmobile, which comprises a drum rotated by means of actuators, the drum forming at least a part of the bearing surface of the ski, the rotation axis of the drum being fitted with bearings in such a way that when the drum rotates, the circumferential surface of the drum moves transversely with respect to the longitudinal axis of the ski, and which drum is provided with one or more ridges protruding from its circumferential surface, the ridges being essentially parallel with the rotation axis of the drum.
2. Description of the Related Art
The type of snowmobile mentioned above, which is equipped with an apparatus for intensifying steering, is known from the Finnish patent 102364 (Vuolle-Apiala). In this known solution, the starting point was to ensure proper turning capabilities of the snowmobile in all possible conditions. Especially on hard and icy surfaces, the turning capabilities of a snowmobile are known to be very poor and the turning radius usually becomes extremely large. In the known solution, this problem has been eliminated by attaching a rotatable drum to the ski, by means of which drum is effected lateral movement of the ski on hard surfaces. The rotatable drums have eliminated the said problem concerning turning capabilities as such, but at the same time compromises have had to be made as far as normal driving with the snowmobile is concerned. Problems are especially the considerable weight of the drums and, on the other hand, the snowmobile""s impaired advancing capacity when driving in the conventional manner, that is, when the intensifying apparatus is not used, because compromises have had to be made in the optimal design of the ski due, on the one hand, to the structure rotating freely during normal operation of the drum and, on the other, to the rotation-symmetrical design of the drum.
The object of the invention is to eliminate the said defects in the known structure.
This object is achieved by means of the arrangement relating to the invention, of which arrangement it is characteristic that the drum is provided with one or more locking means preventing the rotation of the drum, the locking means being arranged to lock the drum into a predetermined position when the apparatus for intensifying steering is not used and, correspondingly, to allow the drum to rotate when the apparatus for intensifying steering is used.
The solution relating to the invention makes it possible for one of the ridges to extend through the bottom of the ski, corresponding to the conventional bottom iron of the ski, when the drum is locked. The arrangement may also be such that only one ridge is designed and made to be such that it will withstand the strains occurring in normal driving of the snowmobile. In such a case, locking is arranged to take place only when the said ridge is at the desired point. Other ridges can be made structurally weaker and thus lighter. It should, however, be noted in particular that in the arrangement relating to the invention, a fully satisfactory solution may in some cases be achieved by using only one ridge per drum.
Irrespective of the number of ridges, in this case, the normal shape of the bottom of the ski is then very nearly achieved. Another preferred embodiment of the invention comes even closer to the normal shape of the bottom of the ski in which it has been arranged that in at least one locking position of the drum, that part of the drum which forms a part of the bearing surface of the ski is designed to substantially correspond to the shape of the bottom of the ski.